Thermally actuated switch



Aug. 6, 1940. c;. w. KUHN El AL 2,210,084

THERMALLY ACTUATED SWITCH Filed March 18, 1938 Patented Aug. 6, 1940UNITED STATES THERMALLY ACTUATED SWITCH Clarence W. Kuhn and Allan P.Charbonneau, Wauwatosa, Wis., assignors to Cutler-Hammer, Inc.,Milwaukee, Wis., a corporation of Delaware Application March 18,

8 Claims.

This invention relates to thermally actuated switches for protectingelectric translating apparatus such as electric motors.

An object of the invention is to provide a simpie, compact and reliablethermally actuated switch unit for protecting an electric motor or othertranslating device under overload conditions.

Another object is to provide a protective switch of the aforesaidcharacter which is responsive to abnormal current conditions in themotor circuit and which may also be associated with the motor in such amanner as to be influenced by heat conditions within the motor.

15 Another object is to provide a cycling overload switch for electricmotors in which a single spring serves to effect snap operation of theswitch and to also eifect resetting thereof.

Another object is to provide a switch of the aforesaid type which canreadily be modified to provide for manual resetting.

Various other objects and advantages of the invention will hereinafterappear.

The accompanying drawing illustrates certain embodiments of theinvention which will now be described, it being understood that variousmodifications may be made in the embodiments illustrated withoutdeparting from the spirit and scope of the appended claims.

In the drawing,

Figure 1 is a vertical sectional view of a switch unit embodying theinvention;

Fig. 2 is a top view taken substantially on line 2-4 of Fig. 1;

Fig. 3 is a perspective view of one end of a cover shown in Fig. 1;

Fig. 4 is a view illustrating an electric motor having a switch unitembodying the invention mounted thereon;

Fig. 5 is a fragmentary side view partly in section illustrating amodification of the switch unit shown in Fig. 1;

Fig. 6 is a sectional view on line 6-6 of Fig. 5;

Fig. '7 is a sectional view similar to Fig. 5 illustrating anothermodification of the switch unit shown in Fig. 1, and

F g. 8 is a fragmentary sectional view on line 8-8 of Fig. '7.

Referring to Figs. 1 and 2, the same illustrate a switch unit includinga snap switch mechanism I having electrothermal actuating meansassociated therewith comprising a thermally responsive bimetallic strip2 and an electric heater 3. Said snap switch mechanism is carried by anelongated insulating base 4 formed of molded material and is mountedwithin a narrow recess 5 in the upper face of said base.

The snap switch mechanism i is made up of stamped sheet metal partscomprising a bracket 6, an operating lever I, a contact lever 8 and a1938, Serial No. 196,616

stationary contact 9. Said mechanism also includes an over-center springIll for effecting snap movement of contact lever i into and out ofengagement with the stationary contact 9 and for being located adjacentthe right hand end of recess 5, and operating lever l is arranged withinan opening IS in projection I4 and is pivotally mounted upon projectionl3. As shown in dotted lines in Fig. 2, the right hand end of operatinglever 1 is formed to provide a tongue l6, and projection I2 is providedwith an opening for receiving said tongue and is notched on oppositesides of said opening as shown at ll to receive knife edged end portionson said operating lever. The upper and lower edges of opening IS inprojection l4 act as stops to limit pivotal movement of operating leverl in opposite directions, and the free end of said operating lever isprovided with an upwardly extending forked projection I8- which islocated to the left of projection l4. Contact lever 8 is bifurcated toprovide spaced arms |9l9 and the side portions of forked projection I8are notched as shown at 20 to receive knife edges on the extremities ofsaid arms Stationary contact 9 1s arranged below the free end of contactlever 8 and said contact lever is movable in opposite directions betweensaid sta tionary contact and a stop projection 2| formed on the lefthand end of recess 5. The over-center spring III is arranged between thearms l9l9 of contact lever 8 and has one end connected to the free endof said contact lever, and its opposite end connected to the upper endof projection l4 on bracket 6. Contact lever 8 is also connected tobracket 6 by a flexible connection 22 having one end soldered to thefree end of said contact lever and its opposite end soldered toprojection l3.

As'is apparent from Fig. 1, spring i0 acts to hold contact lever 8 inengagement with the forked projection l8 on operating lever l and alsoacts to hold said operating lever in engagement with projection l3 onbracket 8. Also as is .apparent from Fig. 1, spring l0 acts to biasoperating lever l upwardly to normally hold the same in engagement withthe top edge of the recess in projection I4. With operating lever i innormal position the pivot of contact lever B is located above the axisof spring Ill and the free end of said contact member is thus normallyheld in engagement with stationary contact 9. 'During downward movementof operating lever l or lower the left hand end of strip 2.

into the dotted line position shown in Fig. 1 the pivot of contact leverB is moved into a position below the axis of spring i 0 and said contactmember is then moved with a snap action under the action of said springout of engagement with stationary contact 9 and into engagement with thestop projection 2|. When operating lever 1 is released the same returnsto normal position under the action of spring l0 and the pivot ofcontact lever 8 is moved into a position above the axis of spring Hi tothereby effect snap movement of said contact lever into engagementwithstationary contact 9. As shown in Fig. 1, an adjusting screw 23 isassociated with the left hand end of bracket 6, said screw beingthreaded into an opening in the bottom wall of casing 3. As is apparent,screw 23 may be adjusted to spring the left hand end of bracket 6 withrespect to the right hand end thereof to vary the normal angularposition of contact lever 8 with respect to spring in and thereby varythe pressure of said contact lever on stationary contact 9.

The bi-metallic strip 2 extends between opposite ends of recess 5 and isarranged to engage the upper end of forked projection it on operatinglever i. The right hand end of strip 2 is supported within an opening inprojection I3 on bracket 6 and the left hand end thereof is slotted toreceive a grooved adjusting screw 23. Screw 26 is threaded within anopening in the left hand end of insulating base ii and is adjustable toraise Heater 3 is arranged above the bi-metallic strip 2 in spacedrelation with respect thereto and is provided with end terminal portionswhich are secured to hollow terminal rivets 25 and 23 passing throughopenings on opposite ends of base 3. As shown in Fig. 1, stationarycontact 9 is secured within a recess in the under side of base l by therivet 26, and said contact is provided with an opening for renderingscrew 24$ accessible for adjustment. The right hand' end of heater 3 isprovided with a terminal element 2! which is held in place by theterminal rivet 25 and said heater is enclosed by a removable cover 28.Cover 28 is U-shapedin cross-section, and as shown in Fig. 3 theopposite ends thereof are cut away as shown at 29 to clear the terminalportions of heater 3. Also as shown in Fig. 3 the end portions of cover28 are provided with opposed projections 30 and as shown in Fig. 2 saidprojections engage shoulders 35 formed on opposite ends of base 3 toreleasably hold said cover in position upon said base.

Referring now to Fig. 4, the same illustrates an electric motor 32having a terminal housing 33 which is provided with a removable coverplate 33. The above described switch unit may be mounted within theterminal housing 33 and when so mounted the same is wrapped in asuitable insulating cover and connected in the motor circuit so that thecurrent supplied to the motor passes through heater 3. As is apparent,when the switch mechanism is in closed position circuit is establishedfrom terminal 21 through the heater 3 to stationary contact 9, andthence through the snap switch mechanism l to terminal l2. Thebi-metallic strip 2 is heated by heater 3 and upon given overloadconditions said strip overcomes the biasing action of spring ID onoperating lever 1 and moves said lever downwardly into circuit openingposition. The motor circuit is thus interrupted, and upon cooling ofbimetallic strip 2' operating lever I returns to normal position toreestablish the motor circuit. In

the embodiment shown in Fig. 3 the operation of the switch is influencedto some extent by heat generated within the motor. By adjusting screw 24the position of the bi-metallic strip 2 with respect to heater 3 can bevaried to vary the current value at which the switch is moved into openposition.

The switch shown in Fig. 1 may be modified as shown in Figs. 5 and 6 toprovide for manual resetting thereof. As shown in Fig. 5 the stop 2|(Fig. 1) is cut away to clear the free end of contact lever 8 and aresetting element 35 comprising a flat insulating bar is slidablymounted within recesses in the side walls of easing 4. Element 35 isheld within said recesses by the cover member 28 and as shown in Fig. 6said element has a push button 36 fixed to the right hand end thereofand is biased to move toward the right by a spring 31 held undercompression between said push button and a washer 38 which bears againstthe right hand side of insulating base 5. Also as shown in Fig. 6element 35 has a shoulder 39 on the left hand end thereof for engagingthe left hand side of insulating base 4 to normally hold said element inthe position shown in the drawing against the action of spring 31. Theunder side of element 35 is provided with a stop surface 50 and camsurface 6|. The stop surface 30 normally engages contact lever 3 uponopening thereof and said stop surface acts to permit movement of saidcontact lever into a position wherein the axis of spring I0 ismaintained abovethe pivot of said contact lever upon return of operatinglever i to normal position. Contact lever 8 is therefore normallymaintained in open position upon return of operating lever i to circuitclosing position. However, upon depression of push button 36 the camportion M on element 35 acts to move contact lever 8 downwardly and withoperating lever l in normal position the axis 40 of spring it is locatedbelow the pivot of contact lever 8 to provide for return of said contactlever to circuit closing position.

In Figs. 7 and 8 resetting of the switch is effected by means of apivoted resetting element 53 comprising a flat insulating bar mountedwithin recesses in the side walls of base 6. As shown in Fig. 8resetting element i3 has its left hand end pivoted as shown at it uponthe left hand side wall of base 6 and the opposite end thereof isprovided with an operating handle '55. Element 33 is biased upwardly bya bow spring 53 held within a recess in the right hand side wall ofcasing i, and is normally held in the position shown in the drawingagainst the action of said spring by cover 21. The resetting element 63normally permits opening movement of contact lever B-into a positionwherein the axis of spring l0 is-maintained above the pivot of contactlever 8 upon return of operating lever i to normal position. Contactlever 8 is therefore normally maintained in open position upon return ofoperating lever 1 to circuit closing position. However, upon downwardmovement of resetting element 63 contact lever 8 is moved downwardly,and with operating lever l in normal position the axis of spring l0assumes a position below the pivot of said contact lever to provide forreclosure thereof.

What we claim as new and desire to secure by Letters Patent is:

1. In an overload protective device, in combination, a fixed support, aswitch operating member movable in opposite directions between extremecircuit closing and circuit opening positions and having one end pivotedupon said support, a

contact element having one end pivoted upon the free end ofsaidoperating member, an over-center spring having one end connected tosaid contact element and its opposite end connected to said support, thepivot of said contact element being movable by said operating memberrelative to said spring to efiect snap movement of said contact elementbetween circuit opening and circuit closing positions, and athermally-actuable member for controlling said switch operating member.

2. In an overload protective device, in combination, a fixed support, aswitch operating member movable in opposite directions between extremecircuit closing and circuit opening positions and having one end pivotedupon said support, a contact element having one end pivoted upon thefree end of said operating member, an elongated over-centcr springhaving one end connected to said contact member and its opposite endconnected to said fixed support, the pivot of said contact element beingmovable by said operating member relative to said spring to eiiect snapmovement of said contact element between circuit opening and circuitclosing positions, said spring being also arranged to constantly urgesaid switch operating member toward circuit closing position, and meansfor controlling said switch operating member including athermally-actuable member.

3. In an overload protective device, in combination, an elongatedoperating member having one end movable about a fixed axis, a thermalelement responsive when heated to move said operating member ,out of agiven normal position, a contact member pivoted upon the free end ofsaid operating member, an elongated over center spring having one endsecured to said contact member, a fixed support for the opposite end ofsaid spring, the pivot of said contact member being normally located toone side of the axis of said spring and being movable into a position onthe oppositeside of said axis by movement of said operating member outof normal position, and said operating member when moved out of normalposition being biased to return to such position under the action ofsaid spring, and means for adjusting said stationary support to vary thenormal angular relation of said spring and said contact member.

4. In an overload protective device, the combination with a snap switchincluding an operating member movable in opposite directions betweencircuit opening and circuit closing positions and biased to move towardthe latter position, an electric heater connected in series with saidswitch, an elongated bi-metal element arranged in heat receivingrelation to said heater and supported at opposite ends, said bi-metalelement tendingwhen heated to bow away from said heater, and beingresponsive upon a given current value in said heater to move saidoperating member into circuit opening position, and means for adjustingsaid bi-metal element with respect to said heater to vary the currentvalue at which said bi-metal element responds to effect opening of saidswitch.

5. In an overload protective device, in combination, an elongatedinsulating base, a snap switch mounted within an elongated opening inone side of said base and having an operating part movable in oppositedirections between extreme circuit opening and circuit closingpositions, said operating part being biased toward circuit closingposition, an elongated electric heater having its opposite ends securedto said base and connected in series with said switch,

an elongated bi-metal element mounted upon said base and arranged inheat receiving relation .to said heater, said bi-metal element beingresponsive upon a given current condition in said heater to move saidoperating member into circuit opening position, and means carried bysaid base for adjusting said bi-metal element with respect to saidheater to vary the current condition at which said bi-metal elementresponds to effect opening of said switch.

6. In an overload protective device, in combination, a pivoted switchmember movable in opposite directions between extreme circuit openingand circuit closing positions, a thermally actuated operating membertherefor, an overcenter spring operatively connecting said switch memberand said operating member to move said switch member out of circuitclosing position with a snap action upon movement of said operatingmember out of agiven normal position, said spring being ineffective toreturn said switch member from circuit opening position to circuitclosing position upon return of said operating member to normalposition, and manual resetting means for rendering said overcenterspring effective to'return said switch member to circuit closingposition but only upon return of said operating member to normalposition.

'7. In an overload protective device, in combination, a pivoted switchmember movable in opposite directions between given extreme circuitopening and circuit closing positions, a thermally actuated operatingmember therefor, a spring for effecting snap movement of said switchmember out of circuit closing position upon movement of said operatingmember in one direction out of a given normal position, saidoperatingmember being constantly biased toward normal position under the actionof said spring, and said spring being ineifective to return said switchmember to circuit closing position upon return of said operating memberto normal position, and manual means for resetting said switch member incircuit closing position through the medium of said spring, but onlyupon return of said operating member to normal position.

8. The combination with a switch having a circuit controlling membermovable in opposite directions between given extreme circuit opening andcircuit closing positions, an electric heater connected in series withsaid switch, a switch operating member having thermal actuating meansassociated therewith subjected to control by said heater, a spring foreffecting snap movement of said contact member out of circuit closingposition upon movement of said operating member in one direction out ofa given normal position under the action of said thermal operatingmeans. said operating member being constantly biased toward normalposition under the action of said spring, and said spring beingineffective to return said contact member to circuit closing positionupon return movement of said operating member to normal position, andmanual means for resetting said contact member in circuit closingposition through the medium of said spring but only upon return of saidoperating member to normal position.

ALLAN P. CHARBONNEAU.

CLARENCE W. KUHN.

